Method for forming contoured composite laminates

ABSTRACT

A composite prepreg laminate such as a hat type-stringer is formed on a contoured mandrel using a combination of mechanical sweeping and vacuum forming.

This application is a divisional application of U.S. patent applicationSer. No. 14/279,275, filed May 16, 2014.

BACKGROUND INFORMATION 1. Field

The present disclosure generally relates to the fabrication of compositestructures, and deals more particularly with a method and apparatus forfabricating concave and convex stiffeners such as stringers, especiallythose that are contoured.

2. Background

Composite laminate structural stiffeners are sometimes required to havecomplex contours tailored to particular applications. For example, inthe aircraft industry, composite laminate stringers used to stiffenaircraft skins are sometimes contoured in one or more planes in order tomatch changes in the geometry of the skins.

Layup and forming of structural stiffeners with complex contours can bechallenging because of the tendency of the uncured composite prepregmaterial to bridge or wrinkle in the areas of contours. Bridging resultsin undesired resin rich-areas in the laminate, while wrinkling mayproduce undesired localized high stress concentrations. In order tominimize these problems, composite laminate structural stiffeners suchas stringers are usually laid up by hand in order to minimize bridgingand wrinkling. However, even using hand layup techniques, bridging andwrinkling of the laminate sometimes occurs which requires hand rework ofthe stiffener, typically using patches. Hand layup of stiffeners andrework of stiffener non-conformities is both labor-intensive andtime-consuming, and therefore expensive.

Accordingly, there is a need for a method and apparatus for laying upand forming contoured composite stiffeners such as composite laminateprepreg stringers, that reduce non-conformities and touch labor. Thereis also a need for a method and apparatus of the type mentioned abovewhich may increase production throughput while reducing factory floorspace required for stiffener production.

SUMMARY

The disclosed embodiments provide a method and apparatus for partiallyautomating the fabrication of composite prepreg laminate stiffeners suchas stringers, which reduces nonconformities and attendant rework, whilereducing touch labor and increasing factory throughput. The disclosedmethod and apparatus employ a combination of mechanical sweeping andvacuum forming to form composite prepreg plies onto complex contours ofa tool without substantial bridging or wrinkling.

According to one disclosed embodiment, an apparatus is provided forforming a composite prepreg laminate. The apparatus includes a mandrelhaving a contoured surface, and a forming head configured to sweep theprepreg ply onto a first portion of the contoured surface of themandrel. The apparatus also includes a flexible diaphragm covering theprepreg ply and configured to vacuum form the prepreg ply onto a secondportion of contoured surface of the mandrel. The forming head includes aplurality of fingers configured to slidably engage and press the prepregply against the first portion of the contoured surface of the mandrel.The fingers may be flexible and include fingertips for individuallyengaging the prepreg ply. The forming head may include a tube having aplurality of slots therein, and the fingers are defined between theslots. The forming head may also include a ram for displacing theforming head. A device is provided for spreading the fingers, which maycomprise a plate adjustably mounted on the forming head and contactingthe fingers. In another embodiment, the device for spreading the fingersis an inflatable bladder. In one embodiment, the forming head includes acam/pivoting mechanism coupled with the fingers for controllingoperation of the fingers. The diaphragm is sealed around its peripheryand forms a chamber capable of being evacuated. The diaphragm may be aflexible vacuum bag which surrounds the prepreg ply and is capable ofbeing evacuated. The forming head may further include a device forsecuring a portion of the prepreg ply against a section of the mandrel.

According to another disclosed embodiment, an apparatus is provided forforming a contoured composite laminate stringer having a hatcross-section and a pair of flanges. The apparatus comprises a contouredelongate mandrel on which at least one composite prepreg ply may beplaced. The mandrel has a cap section, a pair of web sections and a pairof flange sections. The apparatus further comprises a plurality offormer modules. Each of the former modules includes a forming headhaving forming fingers configured to sweep the prepreg ply onto theflange sections of the mandrel. The apparatus also includes or accepts aflexible diaphragm configured to be sealed around its periphery forvacuum forming the prepreg ply against the flange sections of themandrel. The flexible diaphragm may comprise latex that is stretchablesubstantially only in one direction. In one variation, each of theforming heads include a tube having a plurality of slots therein, andthe fingers are located between the slots. The fingers are flexible andare arranged in opposing sets of fingers. A mechanism is provided foradjusting the distance between the opposing sets of fingers. Theorientation of each of the former modules is adjustable. The apparatusmay also include at least one mechanism for aligning the forming headwith local sections of the mandrel. The mechanism adjusts roll, pitchand yaw of the forming head. The apparatus may also include at least onesupport beam, wherein each of the former modules is mounted on thesupport beam.

According to still another disclosed embodiment, an apparatus isprovided for forming a contoured composite prepreg laminate. A contouredmandrel is provided on which at least one composite prepreg ply may beformed. A plurality of former modules are arranged side-by-side forrespectively forming the prepreg ply on the mandrel. Each of the formermodules includes a forming head associated with a section of the mandrelfor forming the prepreg ply on the associated section of the mandrel. Amechanism is provided for aligning each of the forming heads with thecontour of the associated section of the mandrel. The mechanism iscapable of adjusting roll, pitch and yaw of the forming head. Each ofthe former modules includes a frame having a forming head mountedthereon, and the mechanism is capable of pivoting the frame.

According to another disclosed embodiment, a method is provided offorming a composite prepreg laminate. At least one prepreg ply is placedon a contoured mandrel. The prepreg ply is mechanically swept over afirst section of the contoured mandrel, and is vacuum formed over asecond section of the contoured mandrel. The vacuum forming is performedafter the mechanical sweeping of the ply. The method may furthercomprise clamping a third section of the prepreg ply on the contouredmandrel. The mechanical sweeping may be performed by applying pressureto the prepreg ply using the opposing sets of fingers, pressing theprepreg ply against the second section of the mandrel using the opposingsets of fingers, and displacing the opposing sets of fingers as theopposing sets of fingers are pressing the prepreg ply against the secondsection of the mandrel. The method may also include using the opposingsets of mechanical fingers to hold the prepreg ply against the mandrelwhile the prepreg ply is being vacuum formed/consolidated over thesecond section of the mandrel. The mechanical sweeping of the ply may beperformed using a plurality of forming heads. The method also includesaligning each of the forming heads with the contoured mandrel.

According to another disclosed embodiment, a method is provided offorming a contoured composite laminate stringer having a hat section,and a pair of flanges. At least one composite prepreg ply is placed on acontoured mandrel, and then clamped on a cap section of the contouredmandrel. The ply is swept over web sections of the mandrel, while it isheld against an inside radius of the mandrel. The ply is then vacuumformed over flange sections of the mandrel.

The features, functions, and advantages can be achieved independently invarious embodiments of the present disclosure or may be combined in yetother embodiments in which further details can be seen with reference tothe following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the illustrativeembodiments are set forth in the appended claims. The illustrativeembodiments, however, as well as a preferred mode of use, furtherobjectives and advantages thereof, will best be understood by referenceto the following detailed description of an illustrative embodiment ofthe present disclosure when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is an illustration of a perspective view of a composite prepreglaminate stringer having complex contours.

FIG. 2 is an illustration of a sectional view taken along the line 2-2in FIG. 1 showing roll in the stringer, wherein the X-Y plane isindicated by a broken line.

FIG. 3 is an illustration of a sectional view taken along line 3-3 inFIG. 1, showing another roll in the stringer, wherein the X-Y plane isindicated by a broken line.

FIG. 4 is an illustration of a top plan view of the stringer shown inFIG. 1, showing changes in yaw.

FIG. 5 is an illustration of a side elevational view of the stringershown in FIG. 1, showing changes in pitch.

FIGS. 6-12 are illustrations of cross-sectional views of apparatus formechanical sweeping and vacuum forming composite prepreg plies on amandrel having complex contours, respectively showing sequential formingsteps.

FIG. 13 is an illustration of a side elevational view of a ply sweeperalong with a vacuum bagged composite laminate ply.

FIG. 14 is an illustration of an isometric, cross sectional view takenalong the line 14-14 in FIG. 13.

FIGS. 15-18 are illustrations of cross-sectional views of an alternateembodiment of apparatus for mechanical sweeping and vacuum formingcomposite plies on a contoured mandrel.

FIG. 19 is an illustration of a side elevational view of an alternateembodiment of a ply sweeper, portions of the ply sweeper having beenbroken away to reveal a spreader plate.

FIGS. 20 and 21 are illustrations of cross-sectional views showing theply sweeper of FIG. 19 sweeping a ply over a contoured mandrel.

FIGS. 22-24 are illustrations of cross-sectional views showing analternate embodiment of the ply sweeper progressively forming a ply overa contoured mandrel.

FIG. 25 is an illustration of a cross-sectional view showing anotherembodiment of the ply sweeper.

FIG. 26 is an illustration of a cross-sectional view showing a furtherembodiment of the ply sweeper in which the cap is pressed and fingersare held apart prior to sweeping.

FIG. 27 is an illustration of a cross-sectional view showing stillanother embodiment of the ply sweeper in which the sides of the cappresser are pulled toward one another as contact is made with the cap.

FIGS. 28 and 29 are illustrations of cross-sectional views showing afurther embodiment of the ply sweeper progressively forming a ply over acontoured mandrel in which the finger halves are split.

FIG. 30 is an illustration of a cross-sectional view showing a furtherfeature of the split finger ply sweeper in which the finger halvesrotate to sweep the cap and cap/web outside radius prior to fullengagement of the web/flange inside radius.

FIG. 31 is an illustration of a cross-sectional view showing analternate embodiment of the apparatus for mechanically sweeping andvacuum forming plies on a contoured mandrel.

FIG. 32 is an illustration of an end elevational view of one embodimentof a forming unit for forming composite laminate prepreg plies on amandrel contoured in one plane.

FIG. 33 is an illustration of an end elevational view of anotherembodiment of a forming unit for forming composite laminate prepregplies on a mandrel contoured in multiple planes.

FIG. 34 is an illustration of a combined block and diagrammatic view offorming apparatus employing the forming units of the FIG. 33 arrangedside-by-side.

FIG. 35 is an illustration of an end elevational view of a mobile cartinterfacing with a forming station.

FIG. 36 is an illustration of a combined block and diagrammatic view offorming apparatus employing the mobile cart and forming station shown inFIG. 35.

FIG. 37 is an illustration of a perspective view of an alternate form ofa forming apparatus.

FIG. 38 is an illustration of a side elevational view of one of theformer modules shown in FIG. 37.

FIG. 39 is an illustration of a front perspective view of the formingapparatus shown in FIG. 37.

FIG. 40 is an illustration of an isometric view of a portion of theforming apparatus shown in FIGS. 37 and 39.

FIG. 41 is an illustration of a flow diagram of a method of formingcontoured composite prepreg plies.

FIG. 42 is an illustration of a flow diagram of a method of formingcontoured composite prepreg stringers.

FIG. 43 is an illustration of a flow diagram of a method of laying upand forming composite prepreg laminate stiffeners.

FIG. 44 is an illustration of a flow diagram of aircraft production andservice methodology.

FIG. 45 is an illustration of a block diagram of an aircraft.

DETAILED DESCRIPTION

Referring to FIGS. 1-5, the disclosed embodiments relate to a method andapparatus for laying up, forming and handling a composite prepregstructure such as a multi-ply laminate stiffener. The stiffener may be,for example, a contoured composite stringer 50. The stringer 50,sometimes referred to as a hat section 50 includes a cap 56, a pair ofwebs 58, and a pair of flanges 54. An inside radius 60 joins the web andflange surfaces. While a hat type stringer 50 is illustrated, a widevariety of other cross-sectional stiffener shapes may be formed by thedisclosed method and apparatus discussed below. The stringer 50 isformed from laminated plies of a fiber reinforced polymer resin such as,without limitation, carbon fiber epoxy. The stringer 50 may befabricated using plies of unidirectional prepreg that are laid up andformed individually, or in groups (i.e., multiple plies).

The stringer 50 may have one or more complex contours along its length.Any of these contours may be constant or varying. For example, theillustrated stringer 50 has curvatures (see FIGS. 1 and 4) in the X-Yplane, and curvatures (FIG. 5) in the X-Z plane. Portions of thestringer 50 may also be twisted at a constant or varying angle θ (FIGS.2 and 3) in the Y-Z plane. For ease of description hereinafter,curvature in the Y-Z plane will be referred to roll (twist), curvaturein the X-Z plane will be referred to as pitch, and curvature in the X-Yplane will be referred to as yaw.

Referring now to FIG. 6, at least one composite prepreg ply 82 may belaid up and formed on a layup tool such as a contoured elongate mandrel74 mounted on a tool base 84. The mandrel 74 has an outer contouredsurface comprising a first portion and a second portion. The firstportion of the contoured mandrel surface comprises a cap section 76, apair of web sections 78, and inside radii 90. A second portion of thecontoured mandrel surface comprises a pair of flange sections 80. Thecap section 76, web sections 78, inside radii and flange sections 80 allhave substantially the same size, shape and location as the IML (innermold line) of the stringer 50 shown in FIGS. 1-5.

As will be discussed below in more detail, at least one ply 82 is laidup and formed on the mandrel 74 using a two-step process comprisingmechanical sweeping and vacuum forming. The mechanical sweeping of theply 82 is performed by a forming head 64 which is stroked down over theweb sections 78, and the vacuum forming is performed by a vacuummembrane such as, without limitation, a flexible diaphragm 86. As willbecome apparent later in the description, any of a variety of mechanismsand techniques may be employed to perform the mechanical sweeping andthe vacuum forming. As previously noted, in some embodiments, multipleplies 82 may be simultaneously laid up and formed on the mandrel 74.

The forming head 64 includes a ply sweeper 65 which may comprise aplurality of longitudinally spaced mechanical forming fingers 66 thatare arranged in opposing sets thereof. In one embodiment, the formingfingers 66 may be formed of a flexible, resilient material such asplastic, composite, metal etc. The ply sweeper 65 is mounted by suitablehardware 68 to a ram which may comprise, for example and withoutlimitation, a pneumatic piston rod 70. The piston rod 70 drives the plysweeper 65 downwardly 72, causing the forming fingers 66 to initiallyclamp the ply 82 on the cap section 76 in order to maintain alignment ofthe ply 82 relative the mandrel 74 during the subsequent formingprocess. Continued downward movement of the piston rod 70 causes theforming fingers 70 to deflect outwardly while maintaining pressureagainst the ply 82, thereby sweeping the ply 82 down over, andconforming to the web sections 78 of the mandrel 74.

The flexible diaphragm 86 is disposed between the mandrel 74 and theforming head 64. The diaphragm 86 is sealed around its periphery to thetool base 84 by seals 88, forming a substantially vacuum tight chamberaround the flange sections 80. The diaphragm 86 may be formed of asuitable material such as reinforced latex, silicone or the like which,while flexible, is substantially stretchable only in one direction (inthe direction of the X-axis). In some embodiments, the diaphragm 86 maybe a separate element that is manually placed between the forming head64 and the mandrel 74. Alternatively, the diaphragm 86 along with one ormore plies 82 adhered to it may be shuttled together between the forminghead 64 and the mandrel 74. In other embodiments, however, the diaphragm86 may be attached to, and form a part of the forming head 64. In stillother embodiments discussed later herein, the diaphragm 86 may comprisean encapsulating membrane, such as tube-type flexible vacuum bag thatsurrounds the ply layup.

The sequential steps of forming the ply 82 are illustrated in FIGS.7-12, according to one method embodiment. Initially, as shown in FIG. 7,with the tips 75 of the fingers 66 spread apart sufficiently to clearthe cap section 76, the forming head 64 is displaced downwardly 72,causing the fingers 66 to initially clamp a portion of the diaphragm 86and ply 82 against the cap section 76 of the mandrel 74. With the ply 82clamped against the cap section 76, and therefore immobilized, theforming head 64 continues its downward displacement 72, causing thefinger tips 75 to apply pressure to and form the ply 82 down against theweb sections 78 of the mandrel 74, as shown in FIG. 8.

Continued downward movement 72 of the forming head 64, shown in FIGS. 9and 10, causes the ply sweeper 65 to form the ply 82 against theremaining portions of the web sections 78 until the fingertips 75 reachthe inside radii 90 (FIG. 10). At this point, both the cap 56 and thewebs 58 of the stringer 50 fully match the geometry of the web sections78 of the forming mandrel 74. Next, shown in FIG. 11, with thefingertips holding the ply 82 against the mandrel 74 at the inside radii90, the diaphragm 86 is sealed to the tool base 84, and then evacuatedusing a vacuum source 94 to draw air through openings 92 in the toolbase 84.

Referring to FIG. 12, the evacuation of the diaphragm 86 causes thediaphragm 86 to draw the ply 82 down against the flange sections 80 ofthe mandrel 74, thereby completing matching the geometry of the flangesections 80 of the forming mandrel 74. With the shape of the stringer 50having been fully formed, the forming head 64 is raised, and thediaphragm 86 is drawn away, permitting removal of the fully formedstringer 50 from the mandrel 74. In some embodiments, as will bediscussed below in more detail, the mandrel 74 may also be employed totransport and place the completed stringer 50 onto a cure tool (notshown) for curing.

FIGS. 13 and 14 illustrate an embodiment of the ply sweeper 65comprising a tube 96 having a plurality of longitudinally spaced slots98 therein which define two sets of opposing, flexible forming fingers100. The tube 96 may be formed of a flexible, resilient material suchas, without limitation, plastic, and the slots 98 may be formed usingany suitable fabrication process such as sawing or cutting. The opposedflexible fingers 100 have fingertips 102 that are spaced apartsufficiently to clear the cap section 76, as best seen in FIG. 14. Inthe embodiment illustrated in FIGS. 13 and 14, a tube-type vacuum bag105 is sleeved over the plies 82 and the mandrel 74.

When evacuated, the tube-type vacuum bag 105 vacuum forms the plies 82down onto the flange sections (FIG. 12) of the mandrel 74. In someembodiments, compliance of the tube 96 to the shape of the mandrel 74may be achieved by dividing the tube 96 into a plurality of individualsections, each adjustable to match local contours of the mandrel 74. Inother embodiments, however, a single tube 96 extending along the entirelength of the mandrel 74 may be employed to perform the sweeping action.Where a single tube 96 is used, the necessary compliance of the tube 96to changing mandrel contours (roll, pitch and yaw) may be obtained byproviding the top 97 of the tube 96 with flexibility, either bysegmenting the top 97 of the tube 96, or by forming the top 97 of thetube 96 from a flexible material such as a rubber.

Depending upon the type of ply sweeper 65 being employed, it may benecessary to spread the fingertips 102 a distance that is greater thanthe width of the cap section 76 of the mandrel 74. One device forspreading or opening the fingertips 102 is shown in FIGS. 15-18.Referring to FIG. 15, an inflatable bladder 104 is disposed inside thetube 96, as shown in FIGS. 13 and 14. The bladder 104 may be inflatedusing any suitable pressurized fluid, such as air. With the bladder 104fully inflated, as shown in FIG. 15, a lower portion 105 of the bladder104 extends below the fingertips 102.

Referring to FIG. 16, as the forming head 64 is displaced downwardly,the lower portion of the bladder 104 initially contacts the ply 82,clamping it against the cap section 76 of the mandrel 74 in order tomaintain alignment of the ply 82 relative to the mandrel 74 during thesubsequent forming process. When the fingertips 102 clear the capsection 76 and began forming the ply 82 against the web sections 78, thebladder 104 is deflated, as shown in FIG. 17, permitting the fingerforming process to continue. The bladder 104 remains substantiallydeflated until the fingertips 102 have formed the ply 82 down into theinside radii 90, as shown in FIG. 18.

Other techniques may be employed, where necessary, to spread thefingertips 102 a distance that is sufficient to clear the cap section 76of the mandrel 74. For example, referring to FIG. 19, a longitudinallyextending spreader plate 110 may be installed inside the tube 96 andused to open the fingers 100. The spreader plate 110 has threaded studs106 that pass through the top of the tube 96. Wingnuts 108 or similarfasteners on the threaded studs 106 may be adjusted to alter thevertical position of the spreader plate 110. In some embodiments, apower operated device such as a pneumatically or electrically drivenscrew drive (not shown) may be employed in lieu of the wing nuts 108 toprovide automated adjustment of the position of the spreader plate 110.Referring to FIG. 20, as the spreader plate 110 is drawn upwardly inresponse to adjustment of the wingnuts 108, the spreader plate 110engages the inner diameter of the tube 96, forcing the opposing sets offingertips 102 to spread 114 until they clear the cap section 76 themandrel 74. Continued downward movement of the tube 96 (see FIG. 21)allows the fingertips 102 to complete forming of the web sections 58 ofthe stringer 50.

FIGS. 22-24 illustrate another embodiment of the sweeper 65 havingforming fingers 100 similar to those previously described. In thisembodiment, movable forming elements 116 are captured between thefingertips 102 and the ply 82. The forming elements 116 have flatsurface areas 116 a that engage a greater surface area of the ply 82,compared to the embodiments shown in FIGS. 19-21 in which only the outerends of the fingertips 102 engage the ply 82. As the tube 96 isdisplaced downwardly, as shown in FIG. 23, the forming elements 116pivot relative to the fingertips 102, forcing the ply down against theweb sections 78 of the mandrel 74. The forming elements 116 continuepivoting until they form the ply 82 down into the inside radii 90, asshown in FIG. 24.

A variety of other techniques may be employed to clamp the ply 82 to thecap section 76 in order to maintain alignment of the ply 82 relative tothe forming mandrel 74 as the ply 82 is being formed. For example,referring to FIG. 25, a clamping element 120 is mounted on the end of arod 118 that passes through the top of the tube 96. Downwarddisplacement of the rod 118 brings a clamping element 120 into contactwith the ply 82, forcing the ply 82 against the cap section 76. With theply 82 clamped against the cap section 76, the tube 96 is displaceddownwardly relative to the rod 118, allowing the forming fingers 100 tosweep the ply 82 over the web sections 78.

FIG. 26 illustrates another embodiment of the forming head 64 in whichclamping of the ply 82 to the cap section 76 is performed by aspring-loaded clamping member 124 having a clamping surface 128 that isapproximately the same width as the cap section 76. The clamping member124 may comprise, for example and without limitation, rigid plastichaving a hollow core. The use of a relatively broad clamping surface 128may assist in maintaining the cap 56 relatively flat during the formingprocess. The clamping member 124 is attached to a rod 122 surrounded bya compression spring 126 that is trapped between the clamping member 124and the inside surface of the tube 96. As the forming head 64 movesdownwardly, the clamping member 124 makes initial contact with the ply82.

Continued downward movement of the forming head compresses the spring126, which in turn loads the clamping member 124 against the ply 82 andthe cap section 76. As the tube 96 continues its downward movement, thefingers 100 sweep the ply 82 over the web sections 78, and the rod 122is allowed to move up through the top of the tube 96. In someembodiments, as shown in FIG. 27, it may be necessary or desirable toplace a membrane over the bottom of the clamping member 124 to assist inflexing the sides of the clamping member 124 toward the webs as the capis clamped, further providing a smooth transition of the fingers fromthe sides of the clamping member 124 to the webs 78.

Attention is now directed to FIGS. 28 and 29 which illustrate anotherembodiment of the forming head 64 which utilizes a cam mechanism 132 forcontrolling the position of the forming fingers 100 during the plysweeping process. The cam mechanism 132 comprises a cam member 138wedged between a pair of a pair of spreader blocks 134, 136 which act ascam followers that are displaced by downward movement of the cam member138. The spreader blocks 134, 136 are respectively attached to two setsof independent and opposing forming fingers 100. The spreader blocks134, 136 are spring-loaded 135 toward each other, causing fingers 100 tonormally spread apart. However, pressure applied to the spreader blocks134, 136 by the cam member 138 overcomes the force of thespring-loading, forcing the fingers 100 toward each other.

FIG. 28 shows the fingertips 102 spread apart a distance that issufficient to clear the cap section of the mandrels 74. Downwardmovement the cam member 138 (see FIG. 29) causes the fingertips 102 tomove toward each other and sweep ply 82 onto the web sections 78 as theforming head 64 moves downwardly. While a cam mechanism has beendisclosed, a variety of other known mechanism may be employed to controlthe position of the forming fingers 100 during the ply sweeping process.

Attention is now directed to FIG. 30 which illustrates anotherembodiment of the forming head 64 which employs a link mechanism 137 forcontrolling the movement of fingers 100 during a ply sweeping operation.A drive link 131 is pivotally connected to one end of each of twoconnecting links 139, 141. The other ends of the connecting links 139,141 are respectively pivotally connected to a pair of spreader blocks134, 136 that are fixed to two separate, opposed sets of the formingfingers 100. A downward force F applied to the drive link 131 istransmitted through the connecting links 139, 141 to the fingers 100.The fingers 100 rotate 143 in response to the force applied by theconnecting links 139, 141, thereby controlling the movement of thefingertips 102 during sweeping of a ply 82 down over the web sections 78of the mandrel 74. A pair of blocks 145 act as stops that engage thespreader blocks 134, 136 to limit the rotation of the fingers 100.

FIG. 31 illustrates an alternate embodiment of a forming apparatus, inwhich the force used to displace the sweeper 65 is supplied by an outerdiaphragm or vacuum bag 142. In this embodiment, the mandrel 74 ismounted on a tool base 140, along with a pair of sealing blocks 48. Eachof the sealing blocks 148 extends longitudinally along the outer edgesof the flange sections 80 and includes inner and outer seal surfaces150, 152. An inner diaphragm 86 (discussed previously) is placed over aply 82 and is adapted to be sealed against the inner seal surface 150.The outer diaphragm 142 covers the forming head 64 and is sealed to theouter seal surface 152 of blocks 148, forming a vacuum tight outerchamber 167. A caul plate 144 may be placed between the ply sweeper 65and the outer diaphragm 142 in order to concentrate and direct pressureP from the outer diaphragm 142 onto the ply sweeper 65. A pair of vacuumlines 162, 164 pass through the mandrel 74 and are adapted to evacuatethe area beneath the inner diaphragm 86. A third vacuum line 170 iscoupled through a valve 168 to both the ambient atmospheric air 166 andthe vacuum regulator 156. The vacuum line 170 passes through one of theblocks 148 and communicates with outer chamber 167 beneath the outerdiaphragm 142.

In operation, a ply 82 is placed over the mandrel 74, and the innerdiaphragm 86 is placed over ply 82 and sealed to the inner seal surfaces150. The outer diaphragm 142 along with the forming head 64 is thenpositioned over the mandrel 74, and the outer diaphragm 142 is sealed tothe outer seal surfaces 152. A partial vacuum is then drawn on both theinner and outer diaphragms 86, 142 respectively, using vacuum lines 164,170. The partial vacuum in the outer chamber 167 produces a pressure Pthat forces the forming head 64 downwardly, causing the fingertips 102of the ply sweeper 65 to form the ply 82 down over the web sections 78of the mandrel 74.

When the fingertips 102 bottom out at the inside radii 90, a hard vacuumis pulled on the inner diaphragm 86 while the partial vacuum on theouter diaphragm 142 is released through vacuum line 170 and valve 168.The hard vacuum pulled on the inner diaphragm 86 forms the ply 82 downonto the flange sections 80 of the mandrel 74. In order to assist inremoving the sealed inner diaphragm 86, positive pressure may be appliedto the inner diaphragm 86 using the line 162. The inner and outerdiaphragms 86, 142, along with the forming head 64 are then removed toallow the fully formed ply 82 to be removed from the mandrel 74.

It should be noted here that, as previously mentioned, other techniquesand mechanisms can be employed to actuate a stroke of the forming head64 such as, without limitation, clamps, pneumatic cylinders, threadedscrew drives, robots, hoses and outer diaphragms, to name only a few.

Attention is now directed to FIG. 32 which illustrates a portableforming unit 172 that may be used to form a portion of the length of acontoured composite laminate stringer 50. As will be discussed below inmore detail, a plurality of the forming units 172 may be assembledside-by-side to form various portions of the stringer 50 whichrespectively may have differing contours. In the example illustrated inFIG. 32, one or more composite laminate plies (not shown in FIG. 32) areformed on a mandrel 74 having one or more contours in the X-Z plane inorder to form a composite laminate stringer 50 having variations inpitch. In other embodiments, the mandrels 74 may have one or morecontours in the X-Y plane (variations in yaw), and/or one or morecontours in the Y-Z plane (variations in roll).

The portable forming unit 172 broadly comprises a former module 174mounted on a movable platform, which in one embodiment, may comprise amobile cart 188. Other forms of movable platforms are possible,depending on the application. The former module 174 includes a C-shapedframe 175 having a vertical support 176, an upper arm 178, and a lowerarm 180. The former module 174 also includes a forming head 64 mountedon a piston rod 184 of a cylinder 182 for movement along the Z-axis. Thecylinder 182 may be, for example and without limitation part of ahydraulic or pneumatic powered cylinder. The mandrel 74 is removablymounted on the lower arm 180 by any suitable means, such as a handoperated clamp (not shown).

The mobile cart 188 comprises an upright member 190 on which thevertical support 176 is mounted, as well as a cart base 192 havingwheels 194 that allow the cart 188 to be moved over a supporting surfacesuch as a factory floor (not shown). An adjustment mechanism 165 isprovided for adjusting the position and orientation of the former module174 on the upright 190 for movement along the Z axis. In one embodiment,the adjustment mechanism 165 may comprise a screw drive 196 that may bemanually or power driven to adjust the orientation of the former module174 to match the contour of local sections of the mandrel 74.

FIG. 33 illustrates an alternate embodiment of a forming unit 172 thatincludes independent adjustment of the roll, pitch and yaw of a forminghead 64, thereby allowing a composite laminate stringer 50 to be formedthat has complex contours, such as the stringer 50 shown in FIGS. 1-5.The forming unit 172 shown in FIG. 33 is similar to that shown in FIG.32, but additionally has adjustment mechanisms 165 for adjusting thepitch (X-Z plane), roll (Y-Z plane) and yaw (X-Y plane) of the forminghead 64. The adjustment mechanism 165 includes screw drives 198, 206 and208. Roll of the entire former module 174 may be adjusted using screwdrive 206, 208 to adjust the position of slides 202, 204 that supportthe C-shaped frame 175 on a cart upright 190. The yaw of the formermodule 174 may be adjusted using screw drive 198 to rotate the C-shapedframe 175 on the cart upright 190. It should be noted here that variousalternate mechanisms may be used to adjust the yaw, pitch and/or roll ofthe forming head 64 relative to the mandrel 74, and any or all of thesemechanisms may be part of the forming head 64, or part of the formermodule 174 or part of the cart 188. The adjustment mechanisms describedabove provide a form of passive compliance that permits the sweeper 64to be aligned with local contours of the mandrel 74.

A plurality of the forming units 172 of the type shown in FIGS. 32 and33 may be assembled together to collectively form an apparatus forforming a composite prepreg laminate having complex contours. Forexample, referring to FIG. 34, a forming apparatus 195 comprises aplurality of the forming units 172 arranged side-by-side which may bemechanically connected together by suitable mechanical interlocks 185.Each of the forming units 172 is aligned with local contours of theforming mandrel 74 and is operative to form a section of the prepreglaminate. Each of the forming units 172 comprises a former module 174that is associated with a section of the mandrel 74 and is mounted on amobile cart 188, or similar mobile platform. Each of the former modules174 includes the previously discussed features necessary to permitadjustment of yaw, pitch and roll of the forming head 64 tosubstantially match the local contouring of the mandrel 74. The numberof the forming units 172 assembled together will depend upon the lengthof the particular layup mandrel 74 being employed. The use of theindividual forming units 172 permits the forming units 172 to be readilyinterchanged, for repair or service, and provides the flexibility to addor remove forming units 172, as required to suit the particularapplication.

Attention is now directed to FIGS. 35 and 36 which illustrate apparatus205 useful in layup, forming, handling and installation of compositeprepreg laminates such as stringers. The apparatus 205 broadly comprisesone or more forming stations 226, and one or more interfacing mobilecarts 214. Each of the forming stations 226 includes a former module 240provided with a forming head 64 and a mechanism 165 for adjusting theroll, pitch and/or yaw of the forming head 64 to match local contours ofa mandrel 74, similar to the embodiments previously described. Theformer module 240 is mounted on a frame assembly 235 comprising uprights234 and a series of cross members 228, 230, 232. The frame assembly 235may be provided with wheels 194 to facilitate portability of the formingstation 226.

Each of the mobile carts 214 comprises a mandrel support table 216 onwhich at least a portion of a mandrel 74 may be supported. The spacingbetween adjacent ones of the support tables 216 substantially matchesthe spacing between adjacent ones of the former modules 240, such thateach of the support tables 216 is aligned with one of the former modules240. The support table 216 is mounted on one or more uprights 190. Theuprights 190 are attached to vertical frame members 220 that aresupported on a base 192 having wheels 194. The uprights 190 arevertically slidable on the frame members 222 allow the vertical heightof the support table 216, and thus of the mandrel 74 to be adjusted.

In use, the mandrel 74 may be placed on the support table 216 of one ormore of the mobile carts 214, and the carts 214 may be rolled 224 intothe forming station 226, such that the mandrel 74 is aligned beneath theforming head 64. Alternatively, the mandrel 74 may be placed on thecarts 214 after the latter have been rolled 224 into the forming station226. In order to maintain alignment of forming head with the mandrel 74,a mechanical interlock 185 may be provided between the forming station226 and the mobile cart 214. After one or more prepreg plies have beenlaid up and formed in the forming station 226, the cart 214 may be usedto transport the fully formed stringer to another processing stationwhere the carts 214 may be used to handle or manipulate the stringer.For example, the carts 214 may be used to install the formed stringer ina cure tool (not shown).

Attention is now directed to FIGS. 37-40 which illustrate anotherembodiment of the former apparatus 244 which employs features of theembodiments previously discussed. The apparatus 244 comprises aplurality of individual former modules 174 mounted on a common base,which in illustrated embodiment, comprises a center support beam 262.The center beam 262 may be supported on one or more sets of wheels 260which provide the former apparatus 244 with mobility.

Each of the former modules 174 comprises a forming head 64 supported ona C-shaped frame 246. The C-shaped frame 246 includes an upright 248, alower arm 250 and an upper arm 252. A contoured mandrel 74 is removablymounted on the lower arms 250 (FIG. 37) by any suitable mechanism, suchas hand clamps 266. Each of the C-shaped frames 246 is mounted on thecenter beam 262 by a pair of vertical supports 264. The verticalsupports 264 are adjustably connected between the lower arm 250 and thecenter beam 262 by a series of brackets 268 and fasteners 269 receivedwithin ways 270 forming slides. The fasteners 269 (see FIG. 40)selectively fix the brackets 268 in any desired adjustment position.Adjustment of the position of brackets 268 in turn allows adjustment ofthe position of the C-shaped frame 246, and thus of the forming head 64,in both the Y-Z (roll) and X-Z (pitch) planes. Guide rails and linearactuators (not shown) may be employed for moving and adjusting thevertical supports 264 and the lower arm 250.

Each of the forming heads 64 may comprise a ply sweeper 65 attached bysuitable hardware 254 a guide rail 256. The individual ply sweepers 65(tubes 96) are linked together by the C-shaped frames 246 and the centersupport beam 262. The adjustability of the C-shaped frames 246 providesthe apparatus 244 with passive compliance which allows adjustment of thesweepers 64 to match local contouring of the mandrel 74. The guide rail256 is mounted for linear movement along the Z-axis on the outer end ofthe upper arm 252 by two sets of guide rollers 258, A pneumatic drivecylinder 182 mounted on the upper arm 252 has a piston rod 184 attachedto the forming head 64. The cylinder 182 displaces the forming head 64during the forming process, guided by the rail 256. In the illustratedembodiment, the ply sweeper 65 comprises a plurality of forming fingerson a tube 96, however, other embodiments of the ply sweeper 65previously discussed may be used.

Reference is now made to FIG. 41 which broadly illustrates the overallsteps of a method of forming a contoured composite prepreg laminate,such as the stringer 50 shown in FIGS. 1-5. Beginning at step 278, atleast one prepreg ply 82 is placed on a contoured mandrel 74. Then, atstep 280, the prepreg ply 82 is mechanically swept over a first section78 of the contoured mandrel 74. Finally, at 282, the prepreg ply is thenvacuum formed over a second section 80 of the contoured mandrel.

FIG. 42 broadly illustrates the overall steps of a method of forming acomposite prepreg, hat-type stringer 50. Beginning at 284, at least oneprepreg ply is placed on a contoured mandrel 74. At 286, the prepreg ply82 is secured on a cap section 76 of the contoured mandrel 74. At step288, the prepreg ply 82 is swept over web sections 78 of the contouredmandrel 74. At 290, the prepreg ply 82 is held against the inside radii90 of the contoured mandrel 74. With the prepreg ply 82 held against theinside radii 90, then, at step 292, the prepreg ply 82 is then vacuumformed over flange sections 80 of the contoured mandrel 74.

Attention is now directed to FIG. 43 which illustrates a furtherembodiment of a method of laying up and forming composite prepreglaminate stiffeners, such as a stringer 50. At 294, one or more plies 82are laid down on the mandrel 74 and swept over the cap section 76. Heatmay be applied to the plies 82, as required, to soften the plies 82 inpreparation for forming, and/or to assist in tacking them to the capsection 76. Next, at 296, the plies 82 are encapsulated in a vacuummembrane, such as a flexible tube bag 105.

At 298, the mandrel 74 having the plies laid up thereon is transferredto and mounted in a former apparatus 244. At 300, each of the formingheads 64 of the apparatus 244 is aligned with the cap section 76 of themandrel 74. At step 302, a release film such as permeable Armalon® isinstalled over the encapsulated plies 82. In some embodiments, theArmalon® may be integrated into or removably attached to the formermodule 174, thus eliminating the need to perform step 302.

At 304, optionally, the forming fingers 102 are opened a distance thatis sufficient to clear the cap section 76. At 306 forming fingers 102are used to sweep the ply 82 over the web/flange radius of the mandrel74. At 308, the forming fingers 102 are used to hold the plies 82 at theinside radii 90 of the mandrel 74. At 310, vacuum is applied to the bag,resulting in the plies being vacuum formed down onto the flange sections80 of the mandrel 74. At step 312, the forming fingers 102 are retractedwhile vacuum is maintained against the plies 82.

The method described above in connection with FIG. 43 involves sweepingand then vacuum forming each ply 82. Other words, the plies 82 are fullyformed one-by-one onto all sections of the mandrel 74. Alternatively, inanother embodiment, multiple plies, or all of the plies may be sweptover the web/flange radius before the flange sections 80 are vacuumformed. Once the multiple plies have been formed over the web/flangeradius, then the entire group of plies is vacuum formed in order to formthe flange sections 80. In other words, the vacuum forming of the plies82 down onto the flange sections 80 is performed only after all of theplies 82 have been swept over the web/flange radius.

Embodiments of the disclosure may find use in a variety of potentialapplications, particularly in the transportation industry, including forexample, aerospace, marine, automotive applications and otherapplication where contoured elongate composite laminate stiffeners, suchas stringers, may be used. Thus, referring now to FIGS. 44 and 45,embodiments of the disclosure may be used in the context of an aircraftmanufacturing and service method 316 as shown in FIG. 44 and an aircraft318 as shown in FIG. 45. Aircraft applications of the disclosedembodiments may include, for example, without limitation, a variety ofcomposite structural members, including but not limited to stringers.During pre-production, exemplary method 316 may include specificationand design 320 of the aircraft 318 and material procurement 322. Duringproduction, component and subassembly manufacturing 324 and systemintegration 326 of the aircraft to 318 takes place. Thereafter, theaircraft 318 may go through certification and delivery 328 in order tobe placed in service 330. While in service by a customer, the aircraft318 is scheduled for routine maintenance and service 332, which may alsoinclude modification, reconfiguration, refurbishment, and so on.

Each of the processes of method 316 may be performed or carried out by asystem integrator, a third party, and/or an operator (e.g., a customer).For the purposes of this description, a system integrator may includewithout limitation any number of aircraft manufacturers and major-systemsubcontractors; a third party may include without limitation any numberof vendors, subcontractors, and suppliers; and an operator may be anairline, leasing company, military entity, service organization, and soon.

As shown in FIG. 45, the aircraft 318 produced by exemplary method 294may include an airframe 334 with a plurality of systems 336 and aninterior 338. Examples of high-level systems 336 include one or more ofa propulsion system 340, an electrical system 342, a hydraulic system344 and an environmental system 346. Any number of other systems may beincluded. Although an aerospace example is shown, the principles of thedisclosure may be applied to other industries, such as the marine andautomotive industries.

Systems and methods embodied herein may be employed during any one ormore of the stages of the production and service method 316. Forexample, components or subassemblies corresponding to production processfor 324 may be fabricated or manufactured in a manner similar tocomponents or subassemblies produced while the aircraft 318 is inservice. Also, one or more apparatus embodiments, method embodiments, ora combination thereof may be utilized during the production stages 324and 326, for example, by substantially expediting assembly of orreducing the cost of an aircraft 318. Similarly, one or more ofapparatus embodiments, method embodiments, or a combination thereof maybe utilized while the aircraft 318 is in service, for example andwithout limitation, to maintenance and service 332.

As used herein, the phrase “at least one of”, when used with a list ofitems, means different combinations of one or more of the listed itemsmay be used and only one of each item in the list may be needed. Forexample, “at least one of item A, item B, and item C” may include,without limitation, item A, item A and item B, or item B. This examplealso may include item A, item B, and item C or item B and item C. Theitem may be a particular object, thing, or a category. In other words,“at least one of” means any combination items and number of items may beused from the list but not all of the items in the list are required.

The description of the different illustrative embodiments has beenpresented for purposes of illustration and description, and is notintended to be exhaustive or limited to the embodiments in the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art. Further, different illustrativeembodiments may provide different advantages as compared to otherillustrative embodiments. The embodiment or embodiments selected arechosen and described in order to best explain the principles of theembodiments, the practical application, and to enable others of ordinaryskill in the art to understand the disclosure for various embodimentswith various modifications as are suited to the particular usecontemplated.

What is claimed is:
 1. A method of forming a composite prepreg,comprising: placing at least one prepreg ply on a contoured mandrel;mechanically sweeping the prepreg ply over a first section of thecontoured mandrel with a forming head, wherein the forming headcomprises a tube having a plurality of slots therein, and a plurality offingers defined between the slots, wherein the fingers are configured toslidably engage and press the prepreg ply against the first section ofthe contoured surface of the mandrel; and vacuum forming the prepreg plyover a second section of the contoured mandrel with a flexible diaphragmcovering the prepreg ply.
 2. The method of claim 1, wherein vacuumforming the prepreg ply is performed after the mechanically sweeping. 3.The method of claim 1, further comprising: clamping a third section ofthe prepreg ply on the contoured mandrel.
 4. The method of claim 1,wherein: placing at least one prepreg ply includes placing a pluralityof prepreg plies on the contoured mandrel; the mechanically sweepingincludes mechanically sweeping the plurality of prepreg plies over thefirst section of the contoured mandrel; and the vacuum forming includesvacuum forming all of the prepreg plies as a group over the secondsection of the contoured mandrel after the mechanical sweeping.
 5. Themethod of claim 1, wherein mechanically sweeping the plies includes:contacting the prepreg ply with opposing sets of fingers, pressing theprepreg ply against the second section of the mandrel using the opposingsets of fingers, and displacing the opposing sets of fingers as theopposing sets of fingers are pressing the prepreg ply against the secondsection of the mandrel.
 6. The method of claim 5, further comprising:using the opposing sets of mechanical fingers to hold the prepreg plyagainst the mandrel while the prepreg ply is being vacuum formed overthe second section of the mandrel.
 7. The method of claim 1, whereinmechanically sweeping the prepreg ply is performed using a plurality offorming heads, and the method further comprises aligning each of theforming heads with the contoured mandrel.
 8. The method of claim 1,wherein vacuum forming the prepreg ply further comprises: sealing aflexible diaphragm over the prepreg ply to form a substantially vacuumtight chamber; and vacuum forming the prepreg ply onto the secondsection by evacuating the chamber.
 9. A method of forming a contouredcomposite stringer having a hat cross-section, and a pair of flanges,comprising: placing at least one composite prepreg ply on a contouredmandrel; securing the prepreg ply on a cap section of the contouredmandrel; mechanically sweeping the prepreg ply over web sections of themandrel with a forming head, wherein the forming head comprises a tubehaving a plurality of slots therein, and a plurality of fingers definedbetween the slots, wherein the fingers are configured to slidably engageand press the prepreg ply against the web sections of the contouredsurface of the mandrel; holding the prepreg ply against an inside radiusof the mandrel; and vacuum forming the prepreg ply over flange sectionsof the mandrel with a flexible diaphragm covering the prepreg ply. 10.The method of claim 9, wherein holding the prepreg ply is performedwhile the vacuum forming is being performed.
 11. The method of claim 9,wherein the steps of placing a prepreg ply on a contoured mandrel,clamping the prepreg ply, sweeping the prepreg ply, holding the prepregply and vacuum forming the prepreg ply are repeated to form a multi-plylaminate.
 12. The method of claim 9, further comprising: placing aplurality of composite prepreg plies onto contoured mandrel; sweepingeach of the composite prepreg plies over the web section of thecontoured mandrel; and vacuum forming and consolidating all of theprepreg plies as a group over the flange sections of the mandrel. 13.The method of claim 9, wherein mechanically sweeping the plies includes:contacting the prepreg ply with opposing sets of fingers, pressing theprepreg ply against the flange sections of the mandrel using theopposing sets of fingers, and displacing the opposing sets of fingers asthe opposing sets of fingers are pressing the prepreg ply against theflange sections of the mandrel.
 14. A method of forming a compositeprepreg laminate, comprising: arranging a plurality of mobile cartsside-by-side; aligning each mobile cart with local contours of acontoured mandrel, the mobile cart having a former module mountedthereon; placing a local section of the contoured mandrel on each formermodule of the arranged mobile carts; placing at least one prepreg ply onthe contoured mandrel; and forming the prepreg ply on the contouredmandrel, including using each former module to form a local portion ofthe prepreg ply.
 15. The method of claim 14, wherein forming the prepregply further comprises: mechanically sweeping the prepreg ply over afirst section of the contoured mandrel.
 16. The method of claim 15,wherein mechanically sweeping the prepreg ply comprises: contacting theprepreg ply with opposing sets of fingers; pressing the prepreg plyagainst a second section of the mandrel using the opposing sets offingers; displacing the opposing sets of fingers as the opposing sets offingers are pressing the prepreg ply against the second section of themandrel; and mechanically sweeping the prepreg ply over the firstsection of the contoured mandrel using the displaced opposing sets offingers.
 17. The method of claim 16, further comprising: vacuum formingthe prepreg ply over the second section of the mandrel; and holding theprepreg ply against the mandrel using the opposing sets of fingers whilethe prepreg ply is being vacuum formed.
 18. The method of claim 14,wherein each former module comprises a forming head, collectively aplurality of forming heads, the method further comprising: aligning eachof the forming heads with the contoured mandrel; and mechanicallysweeping local portions of the prepreg ply over a first section of thecontoured mandrel with a corresponding one of the plurality of formingheads.
 19. The method of claim 18, wherein each forming head comprisesopposing sets of fingers, collectively a plurality of opposing sets offingers, wherein mechanically sweeping the prepreg ply comprises:contacting local portions of the prepreg ply with a corresponding set ofthe plurality of opposing sets of fingers; pressing the prepreg plyagainst a second section of the mandrel using the plurality of opposingsets of fingers; displacing the plurality of opposing sets of fingers asthe plurality of opposing sets of fingers are pressing the prepreg plyagainst the second section of the mandrel; and mechanically sweeping theprepreg ply over the first section of the contoured mandrel using thedisplaced plurality of opposing sets of fingers.
 20. The method of claim19, further comprising: sealing a flexible diaphragm over the prepregply to form a substantially vacuum tight chamber; and vacuum forming theprepreg ply over the second section of the mandrel.